The present invention relates to a dressing apparatus for performing in-process electrolytic dressing on a grinding stone which is engaged in a process.
Conventionally, when a process is performed using a grinding stone made from a conductive base material, the so-called electrolytic in-process dressing is performed, i.e., the grinding stone is subjected to in-process electrolytic dressing during the ongoing process for purposes such as preventing the grinding stone from causing clogging (hereinafter referred to as "ELID grinding").
As shown in FIG. 10, ELID grinding is a process of performing electrolytic dressing on a grinding stone 1 by applying electricity to a grinding fluid filled between a grinding stone 1 and an electrode 2 having an arcuate inner surface to cause electrolysis which elutes the base material of the grinding stone 1.
In the above-described process, the grinding stone 1 and the electrode 2 are set as positive and negative poles, respectively, and a grinding fluid having low conductivity is used and supplied to the gap between the grinding stone 1 and the electrode 2 through a nozzle which is not shown.
In summary, in ELID grinding, an appropriate amount of base material of the grinding stone 1 is eluted by means of anodization to keep the amount of the abrasive grains that are projected constant.
During such conventional ELID grinding, as the grinding stone 1 is worn as the processing on the workpiece using the grinding stone 1 proceeds, the gap between the electrode 2 and the grinding stone 1 is expanded accordingly. This results in a need for sliding the electrode 2 toward the grinding stone 1 (in the direction indicated by the arrow A in FIG. 10) repeatedly to adjust the gap.
However, if the grinding stone 1 becomes smaller as shown in FIG. 11 as a result of wear, there will be a difference between the curvature of the outer circumference of the grinding stone 1 and the curvature of the inner arc of the electrode 2. This results in a similar variation in the width of the gap between the grinding stone 1 and the electrode 2. In particular this gap is maximized at the side of ends 2a of the electrode 2.
For example, in the case of an electrode of 90.degree. as shown in FIG. 12 wherein the diameter of the grinding stone, the diameter of the electrode, and the gap between the grinding stone and the electrode are set at 150 mm, 150 mm; and 0.3 mm, respectively, the gap between the grinding stone and the electrode is expanded to a maximum of 0.79 mm when the grinding stone is worn to a diameter of 146 mm.
As a result of such expansion of the gap, the area of the electrode 4 effective for ELID grinding is reduced; initial efficient dressing can not be maintained; a non-conductor film having a sufficient thickness can not be produced in the area where the base material is eluted; and the stability of the ELID grinding can not be maintained.
Further, in conventional ELID grinding, dressing conditions significantly vary depending on the diameter of the grinding stone even if a brand-new grinding stone is used. Specifically, if conventional ELID grinding is applied to a grinding stone having a small diameter which is different from the grinding stone 1, the width of the gap between the grinding stone of a small diameter and the electrode 2 will fluctuate for reasons associated with the curvature of the inner arc of the electrode. This reduces the area of the electrode 2 effective for ELID grinding and results in significant changes in dressing conditions. As a result, a problem arises in that initial efficient dressing can not be maintained and in that only a limited range of grinding stones can be used.